1. Field of the Invention
The present invention relates to a nailer and a bumper provided therein for braking a motion of an impact piston.
2. Description of the Related Arts
Generally, a bumper provided within a nailer is disposed at a lower portion of an impact cylinder, which slidably houses an impact piston. Said bumper is used for braking the impact piston by receiving a bottom surface of the actuated impact piston when the nailer is driving in a fastener such as a nail. The term "nailer" means of an apparatus that includes so called a "tacker" for driving a staple in as well as an apparatus for driving in a various types of nails. In order to absorb an impact efficiently that is made by the impact piston, a volume of the bumper is desirably large. However, in case an outer diameter of the bumper is greater than that of a diameter of the impact piston, an upper surface of the bumper 10 is cracked due to the impact made when it is striked, as shown in FIG. 5(a), and the bumper is damaged. Particularly, in the case where a nailer with the impact piston of a small diameter is used, the bumper 10 may be also small. Therefore, a central hole of the bumper for inserting the driver of the nailer is deformed in accordance with the configuration of the driver, further, a reinforcement to thin parts of the deformed shape caused by the deformation is required. A transverse section of the driver 11 is formed in a rectangular shape so that a transverse section of a central hole 12 of the bumper 10 for inserting the driver 11, as shown in FIG. 5(b), is formed in an elliptic configuration to surround the driver 11.
However, in the case where the central hole 12 has the elliptic shape, a stress concentrates on the thin parts of the bumper 10 when the impact is made thereon by the impact piston. Therefore, it was difficult to design the bumper due to the of obtaining an equally distributed balance of load. Further, there was a problem that the performance of absorption and the durability of the bumper were not efficiently developed in reference to the increase in size.
Accordingly, with regard to a nailer by the use of high-pressurized compressed air whose output energy is large when it strikes a nail, and has a small diameter piston, it was difficult to obtain a sufficient size for the bumper. Therefore, it has been very difficult to design a bumper with good performance of absorption and durability.